Dissociated dopaminergic neurons from substantia nigra zona compacta in young rats lack functional NMDA receptors.
Glutamate-mediated excitotoxicity plays an important role in the degeneration of nigrostriatal dopamine (DA) neurons induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), although the role of the N-methyl D-aspartate (NMDA) receptor subtype in this process is still uncertain. We studied glutamate receptor subtype agonist-induced ionic currents in acutely dissociated DAergic neurons from the rat substantia nigra zona compacta (SNc) using the nystatin-perforated patch-clamp whole-cell recording technique. The results fall into four main categories. First, single neurons, freshly isolated from SNc, exhibited a large soma and multipolar morphology, responded to DA, and stained positively for tyrosine hydroxylase (TH). Second, rapid application of L-glutamate (> 10(-5) M) induced an inward current with minimal desensitization at a clamp voltage of -60 mV. Third, kainic acid (KA) or alpha-amino-3-hydroxy-5-methyl-isoxazole (AMPA) induced an inward current that was similar to the glutamate-induced current while, in the same neuron, NMDA (10(-4) M) failed to induce any current response in Mg2+-free solution that contained 10(-5) M glycine at a clamp voltage of -60 mV. Under the same experimental conditions, NMDA induced a clear current response in isolated substantia nigra reticulata (SNr) neurons. Fourth, the specific NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (APV, 10(-4) M) failed to block 10(-4) M glutamate-induced inward current, while the specific KA/AMPA receptor antagonist 6-cyano-7-nitroguinoxaline-2, 3-dione (CNQX, 10(-5) M) completely blocked the glutamate-induced current. These results indicate that in single SNc DAergic neurons of 2-week-old rats, L-glutamate-induced inward current is mediated by non-NMDA receptors rather than by NMDA receptors.
Wu
J
J
Departments of Neurology and Neurosciences, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA.
Partridge
L D
LD
D000818:Animals; D004298:Dopamine / Q000378:metabolism*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D007476:Ionophores; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D009761:Nystatin; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000187:drug effects / Q000502:physiology; D018092:Kainic Acid Receptors / Q000187:drug effects / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*; D013378:Substantia Nigra / Q000166:cytology / Q000378:metabolism / Q000502:physiology*
D004298:Dopamine; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D007476:Ionophores; D009761:Nystatin; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate